>Should AH and ESP both have a fixed size replay counter ? (Yes/No/Don't Care) Yes. >If they have a fixed size counter, what size should it be? (32 bits/64 bits) 32-bits, using whatever padding is necessary to achieve the required alignment for IPv6 >Should SHA-1 output be truncated to 128 bits from 160 bits ? (Yes/No/Don't Care) Don't care (don't know enough about the underlying merits).